1. Technical Field
This invention relates to push rods for engines and, in particular, to one-piece push rods especially applicable for use in automotive high speed, high compression ratio internal combustion engines equipped with high lift cams.
2. Discussion
Push rods are conventionally used between a rocker arm and cam follower in an internal combustion engine to control the opening and closing of valve seats in the engine cylinders. The following patent documents disclose a wide variety of push rod constructions: U.S. Pat. Nos. 1,594,471; 1,663,191; 1,823,419; 1,948,415; 2,019,444; 2,434,080; 2,743,712; 2,818,843; 2,851,980; 2,857,895; 2,897,805; 2,960,080; 3,034,488; 3,086,507; 3,468,007; 3,549,853; 3,789,650; 4,218,996; 4,317,267; 4,436,063; 4,453,505; Canadian patent Nos. 479,834; 640,247 and Japanese Patent Nos. 55-1446; 55-46025, 55-146,211; and 59-225844.
Hollow tubular push rods are desirable because they are generally stronger and stiffer than a solid rod of the same weight. One-piece hollow push rods having 180.degree. hemi-spherical seats have been sold by the inventor of the present invention. These push rods consisted of elongated straight walled tubes having 180.degree. hemi-spherical ends that were cold formed using a combination of a special forming tool and a punch similar to the ones disclosed in FIGS. 4 and 6 herein. An alternative to straight-walled push rods is described in U.S. Pat. No. 4,850,315, which is assigned to the same assignee as this present invention. More particularly, a single piece push rod is disclosed in the form of an elongated hollow tube having a middle portion with a larger outer diameter than the tube has near its ends. In a particular embodiment, the middle and end portions of the tube are cylindrical while the surfaces bridging the middle and end portions are tapered.
While such one-piece push rods have generally proven satisfactory, the present invention provides improvements thereto that are expected to provide increased performance characteristics especially when installed in engines having high lift cams. These characteristics are achievable without requiring the use of a multiple piece construction, such as the use of inserts or the like, at the ends of the push rods as disclosed in some of the above-mentioned patent literature.